How can I extend the Guard class?

[lkomanetz]

There are guard conditions that are specific to the domain I'm working in that I want to add to the Guard class. The intent is to keep all guard clauses using the same style. In my case it is a condition ensuring that positions of two things don't cross (so the one on the top isn't trying to go below the item on the bottom).

So something like Guard.DoNotCross(pins);

I have tried creating a partial class with the same name in the same namespace but then I get other issues. Is there a way to extend this or do I have to create my own class?